Interannual Variability of Pteropod Shell Weights in the High-CO2 Southern Ocean

Interannual variability of pteropod shell weights in the high-CO2 Southern Ocean

Donna Roberts, Will Howard, Andrew Moy, Jason Roberts, Tom Trull, Stephen Bray & Russ Hopcroft

Antarctic Climate & Ecosystems Australian Government Cooperative Research Centre Department of Climate Change Motivation for Research Project

• Atmospheric CO2 ⇑

• Ocean pH ⇓ 2- • [CO3 ] ⇓

. models suggest polar regions 2- will experience [CO3 ] below those favourable for aragonite precipitation first 1

. Southern Ocean a good place to look for impacts of ocean acidification on aragonite calcifiers

1 Orr et al. 2005. Nature: 437 Southern Ocean shelled pteropods: now

SAZ-SENSE Voyage CEAMARC Voyage 44-54°S 140-155°E 62-67°S 138-146°E 17 Jan - 20 Feb 2007 23 Jan - 16 Feb 2008 1 2 3 1 2 1. Cavolinia tridentata f. atlantica

2. Clio cuspidata

3. Clio pyramidata f. antarctica

4 5 6 4. Clio pyramidata f. sulcata 5. Clio balantium (recurva)

6. Diacria rampali

7. Limacina helicina antarctica 7 8 9 8. Limacina retroversa australis * 9. Peracle cf. valdiviae * 1. Limacina helicina antarctica 2. Clio balantium Southern Ocean shelled pteropods: past

• Sediment Traps . 47°S . 142°E . 2000 m trap . 4500 m water . 1997/98 - 2005/06

. each cup (21) treated with dense, buffered, * biocide solution and open from 5 - 60 days Southern Ocean shelled pteropods: past

• How will we measure calcification response in Southern Ocean pteropods?

2- 1 . Foram shell weights ⇓ as surface water [CO3 ] ⇓ 1 mm . Pteropod shell weights?

- recovered 5 traps in 9 years at 47°S - extracted 150µm - 1mm size fraction

- dissolved organics in buffered 3% H2O2 - identified whole pteropod shells - batch weighed discrete taxa per cup (microbalance precision = 0.1µg) - accounted for non-uniform trap intervals

1 Barker & Elderfield. 2002. Science: 297 Southern Ocean shelled pteropods: past

• Sediment Trap Pteropods

. Limacina helicina antarctica (66%)

. Limacina inflata (14%)

. Clio (pyramidata, sulcata, cuspidata)*(10%)

. Limacina retroversa australis (2%)

1 mm Southern Ocean shelled pteropods: past

• Limacina helicina antarctica . Antarctic coast <---> Subtropical Front

. forma antarctica 1 mm - Antarctic waters - Antarctic coast <---> Polar Front - ‘cold’ morphotype (25%) 1

. forma rangi 1 mm - Subantarctic waters - Polar Front <---> Subtropical Front

- ‘warm’ morphotype (41%) 1

1 van der Spoel & Dadon. 1999. Pteropoda: Boltovskoy (ed) South Atlantic Zooplankton 1 mm Limacina helicina antarctica f. antarctica

• Shell weight change

n = 53

n = 3 n = 11 n = 29 n = 1

Linear rate (P=0.02) reduction in calcification -1 -1.17 ± 0.47 µg yr ≈ 35% Limacina helicina antarctica f. rangi

• No shell weight change

n = 13 n = 7 n = 78

n = 25

n = 35 Southern Ocean pteropod flux

• Shell flux to sediment traps Causal mechanism(s)?

. physical . ecological . biogeochemical - sea surface - primary - carbonate ion temperature production availability

1 2

2- * ~25% drop in [CO3 ] from pre-ind’l 2- ** ~5% drop in [CO3 ] past decade

1 Smith & Reynolds. 2004. J. Climate:17 3 Feely et al. 2004. Science: 305 5 CLIVAR/WOCE SR3 voyages 2 SeaWiFS. 2008. NASA 4 Sabine et al. 2004. Science: 305 6 McNeil et al. 2001. JGR: 106 Hypotheses

• The reduction in carbonate ion in • forma antarctica is morphologically the Subantarctic Southern Ocean and ecologically distinct from forma is affecting Limacina helicina rangi and we propose they have distinct antarctica forma antarctica’s physiological responses to calcification ability to calcify

* our challenge is to find pre- industrial pteropods: not as • our results provide a • our results have implications easy to source as forams or benchmark* against which for intra-specific calcification coccoliths in the Southern Ocean future calcification change in responses** to changing ocean Southern Ocean pteropods chemistry (cf.1,2) ** we recommend separating forma antarctica from forma may be measured rangi in future experiments

1 Cubillos et al. 2007. MEPS: 348 2 Fabry. 2008. Science: 320 Conclusions

* Limacina helicina antarctica forma antarctica • Pteropods are important indicators of calcification in the Southern Ocean

• The rate of shell weight change in forma antarctica is not of trivial concern:

South of the Antarctic Polar Front pteropods* sometimes dominate the export flux of calcium carbonate 1

-1.17 ± 0.47 µg yr-1 ------> 1 Collier et al. 2000. Deep-Sea Res. II: 47 Thanks

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